Replacing Aging Gas Pipeline Infrastructure in Karst - The WB Xpress Project

Building and maintaining vital infrastructure such as gas pipelines through miles of land with numerous karst features requires ingenuity and expertise to avoid pitfalls that affect construction and the long-term performance as well as the environment.

In 2015, Columbia Gas/TC Energy proposed to construct approximately 30 miles of various diameter pipeline,  construct two new compressor stations, modify seven existing compressor stations, and increase the maximum allowable operation pressure on various segments in Virginia and West Virginia. This project, called The WB Xpress Project, included the “lift and replace” of segments of pipe that were more than 50 years old.

Karst is a landform type, characterized by the presence of sinkhole, caves, large springs and a highly irregular “pinnacled” bedrock/soil interface. It is a consequence of the presence of soluble bedrock, primarily limestone, dolomite and marble; but it also can develop in evaporite rocks including gypsum and halite (i.e. rock salt).

Terracon was commissioned to identify karst features along the proposed alignment (such as sinkholes, caves, springs, and stream crossings in karst-forming bedrock) due to the potential impact of pipeline repair and replacement activities on the karst aquifer and for the possible development of sinkholes or subsidence to potentially affect the integrity of the pipeline.

Understanding the Structural and Facility Impacts of Karst Geohazards

The geohazards presented by karst terrain greatly differ from other natural settings. Natural and human-induced subsidence and sinkholes, slope movements favored by karst conduits and caves, flash floods related to inability of the system to manage water from heavy rainstorms, and pollution caused directly or indirectly by human actions are the main types of geohazards typical of karst terrains. The karst geohazard can affect both structures and facilities, as well as human health and the environment.

Industry-Leading Karst Management and Practices

Terracon has been leading the way in the development of a standardized method for karst survey, remediation, and management, which safeguards both the integrity of the installation and the conservation and protection of the subsurface habitat and karst aquifers. Over the last 11 years, Terracon has worked closely with the Federal Energy Regulatory Commission, U.S. Fish and Wildlife Service, the National Forest Service, and state departments of environmental protection to develop a protocol that has now become widely accepted as the industry standard for pipeline assessment in karst terrain. The elements of this method are:

• Pre-Construction Assessment and Field Survey – Describes in detail the pre-construction database and remote sensing review, as well as field survey methods and procedures which will be used.
• Construction Monitoring Protocols – Describes the methods and procedures used during the construction phase of the project, the activities to be conducted by the field geologist during excavation and trenching activities, including how the observations will be made, and the reporting format and frequency.
• Karst Mitigation and Conservation Procedures – Discusses the best management practices to be used for mitigating, remediating, and minimizing impacts to and/or from karst features that may be encountered during construction activities. This includes features that either are within, or receive drainage from, the pipeline right-of-way, or features that are intercepted during the excavation and trenching process, as well as access roads, additional temporary workspace areas, or any other areas where land disturbance necessary for pipeline construction is planned.

WB Xpress – A Successful Project

The WB Xpress project was  completed in 2019, and now transports approximately 1.3-billion cubic feet per day of natural gas to supply the increasing demand in northern Virginia and West Virginia.

Over 300 acres of access roads, temporary workspaces, and staging areas were assessed during the construction phase of the project, and these workspaces were returned to pre-construction condition after completion of the project. The project’s karst management and conservation efforts successfully prevented any known construction impacts to the karst resource.